1. Field of the Invention
The present invention relates generally to broadcasting/communication systems, and more particularly, to a method and apparatus for transmitting and receiving data including a plurality of data streams by multiplexing different efficiency modes in broadcasting/communication systems.
2. Description of the Related Art
Modern broadcasting/communication systems typically employ physical layer configurations for transmitting data that have a variety of parameters, which are typically chosen at the system design stage, as a compromise between efficiency in relation to system capacity and robustness in terms of expected reception conditions. For example, a physical layer configuration characteristic may relate to a number of subcarriers used by a multicarrier transmission scheme, a multiple antenna scheme such as a Multiple-Input, Multiple Output (MIMO) scheme, a guard interval between symbols to allow for settling of multipath, and/or a distribution of pilot signals within transmitted symbols. Such physical layer configuration characteristics are typically uniform within each entire individual symbol of a transmission, and therefore, such characteristics may be called macro-configuration characteristics.
Wireless systems involving uni-cast transmission and a reverse link, such as a cellular wireless communication system or a wireless access system such as Institute of Electrical and Electronics Engineers (IEEE) 802.16 Wimax, may employ adaptive modulation and coding in order to optimize settings according to the trade-off between efficiency in relation to system capacity and robustness in terms of expected reception conditions for a given user; the reverse link, or uplink, may be used to communicate the signal reception conditions for a given user to a base station, and the communication system may choose an appropriate modulation and coding scheme for each user, that may be adapted as conditions change. A modulation scheme may for example relate to a Quadrature Amplitude Modulation (QAM) constellation size, and a coding scheme may relate to a coding rate or code word length; either or both of which may vary between subcarriers of a symbol in a multicarrier system such as Orthogonal Frequency-Division Multiplexing (OFDM). A modulation and coding scheme may be referred to a micro-configuration characteristic. Typically, in cellular wireless communication systems and wireless access systems, macro-configuration characteristics are the same among different users, and the micro-configurations may be adapted on per-user basis, in cases where the system allows such configurations.
Unidirectional broadcast systems typically transmit signals that may potentially be received by any user. Unidirectional broadcast systems also lack a reverse link. Therefore, adaptive modulation and coding is not typically employed in unidirectional broadcast systems.
Digital Video Broadcasting (DVB) systems, such as second generation of DVB systems known as DVB-Terrestrial 2 (DVB-T2), DVB-Cable 2 (DVB-C2) and future DVB-Next Generation Handheld (DVB-NGH) systems typically use OFDM modulation. Different configurations (e.g. Fast Fourier Transform (FFT) sizes, guard intervals, pilot patterns, etc.) are usually specified in these systems, each intended to achieve a given efficiency for a given deployment scenario. Network operators then have options for selecting the best configurations suitable for various deployment scenarios. Although broadcast systems cannot adapt dynamically to the users' instantaneous reception conditions, the concept of Physical Layer Pipes (PLPs) with different levels of efficiency and robustness, typically in terms of modulation and coding scheme, has been introduced in the 2nd generation DVB systems. Such systems are able to offer different levels of Quality of Service (QoS) as required for the transport of the different kinds of services in the system. However, in such systems each user of a service is provided with a signal with the same modulation and coding scheme for the service, as well as the same macro-configuration of the physical layer. Trade-offs between efficiency in relation to system capacity and robustness in terms of reception conditions are therefore typically set as a compromise value for all users.